The skeletal system is the most important organ system for studying vertebrate morphology. It provides shape, support, and protection to the body. The skeletal system consists of two main parts - the axial skeleton which includes the skull and vertebral column, and the appendicular skeleton. The axial skeleton gives the body its basic form and protects the spinal cord and vital organs. It develops from cartilage that later ossifies into bone. The skull is made up of the neurocranium, dermatocranium, and splanchnocranium. Vertebrae come in different shapes depending on the number and fusion of centra. Ribs attach to vertebrae and form a protective rib cage in most vertebrates

1. Skeletal System of
Vertebrates
Botones, Maria Elena S. Gaba, Chinee Anne Marie C.
Kiamzon, Kristelle Ann A. Ortilla, Zsazsa D.
Pascual, Leah Mae S.

2. SKELETAL SYSTEM

3. Skeletal System
 Most important organ system in the study of
vertebrate morphology.
- Provides reliable information about the
specific adaptations of vertebrates such as
posture and locomotor adaptations
- Tells about other organ systems
- Due to its hardness and durability, skeleton
becomes fossilized and the study of past
vertebrate life is mostly based on fossils

4. Functions
 Give shape to the body and support its
weight
 Offers a system of levers that aid
muscles to produce contraction
 Protects soft parts such as nerves, blood
vessels and other viscera
 Two types of skeleton
 Exoskeleton (protective structure on
the outside of the body)
 Endoskeleton (protective structure
on the inside of the body)

5. Endoskeleton

6. Exoskeleton

7. Functions
 Two separate components
 Cranial skeleton or the skull
 Postcranial skeleton (axial and
appendicular)
 Composed of mineralized connective
tissues ( dentin, enamel, cartilage and
mostly bones)
-mesenchyme differentiated into
scleroblasts which give rise to
osteoblasts, odontoblasts,
chondroblast and ameloblast.

8. Cartilage
- Forms an important part of the endoskeleton in all
vertebrates
- Cartilage is avascular tissue,
- Other types include the elastic cartilage in the external ear
and epiglottis, and fibrous cartilage in the intervertebral discs
and attachment of tendons and ligaments.
- Cartilage is a tough, elastic, fibrous connective tissue found in
various parts of the body, such as the joints, outer ear, and
larynx. A major constituent of the embryonic and young
vertebrate skeleton, it is converted largely to bone with
maturation.

9. Bones
 Comprise most of the endoskeleton in
higher vertebrates
 Contrary to cartilage, blood vessels and
nerves are present in bony tissues
passing through small Haversian canals.
 Haversian canals are located in the bone
tissue at the center of the compact bone
through which blood vessels, nerve
fibres and lymph vessels pass.

10. Bones
 Organic component is primarily collagen, which gives
bone great tensile strength
 Inorganic components of bone comprise 60% of the dry
weight
 Functions:
- Support and movement via attachments for soft tissue
and muscle
- Protects vital organs
- Major site for red marrow for production of blood cells
- Plays a role in metabolism of minerals such as calcium
and phosphorus

11. Bones
2 basic structural types
based on bone tissue
- Compact bone
- Spongy bone or
cancellous bone
Periosteum – dense layer
of connective tissue that
surrounds the bone

12. As to kind of bone tissue

13. Cranial Skeleton
Skeletal framework
of the head (skull)
3 embryonic
components:
1. Chondrocranium
2. Dermatocranium
3. Splanchnocranium

14. Chondrocranium
Composed of cartilage which contributes
to the base of the skull, includes the
sense capsule and in most vertebrates, is
replaced by bone
Primary brain case
Surrounds the brain and the special
sense organs

15. Chondrocranium Ossification Centers
 Occipital centers - cartilage surrounding
the foramen magnum may be replaced by
as many as four bones: one basioccipital, two
exoccipital, and one supraoccipital
 The six centers that we can see on diagram are:
 - Basioccipital bone;
 - Exoccipital bone (two centers);
 - Supraoccipital bone;
 - Interparietal bone (two centers).

16. Sphenoid centers from
basisphenoid bone,
presphenoid bone, and the
side walls above
basisphenoid and
presphenoid form
orbitosphenoid,
pleurosphenoid and
alisphenoid.

17. Ethmoid centers tend to remain
cartilaginous and form cribiform plate of
ethmoid and several ethmoturbinal bones
Otic centers – the cartilaginous otic
capsule is replaced in lower vertebrates by
several bones: prootic, opithotic, epiotic

18. Types of Skull Based on Fenestrae (Temporal Openings)
1. Anapsid skull
- The primitive skull, has no temporal fenestra,
possessed by turtles and other primitive reptiles.
2. Diapsid skull
- The diapsid skull has two temporal fenestrae,
possessed by most members of diapsida including
crocodiles, birds and lizards.

19. 3. Euryapsid skull – this is a derived
diapsid
skull where the lower temporal
fenestra is lost
4. Synapsid skull – has one fenestra
located in
a different place than the euryapsid
skull

20. Dermatocranium
Composed of dermal bones that overlie the
chondrocranium and splanchnocranium
Forms the sides and roof of the skull
protecting the brain, it also forms most of
the bony lining of the roof of the mouth
and encases much of the
splanchnocranium
Completes the protective cover of the brain
and jaws

21. Parts of Dermatocranium
Modern fishes and amphibians have simple skull
and the number of dermal bones present is
reduced, some have tended to be lost or fused
In amniotes, dermal bones predominate, forming
most of the braincase and lower jaw; they are
divided into six series of bones.

22. Parts of Dermatocranium
1. Facial Series – encircles the external naris forming
the snout.
2. Orbital series – encircles the eye defining the orbit
3. Temporal series – lies behind the orbit completing
the posterior wall of the braincase
4. Vault series or roofing bones – located across the
top of skull covering the brain beneath
5. Palatal series – dermal bones of the primary palate
covering the roof of the mouth
6. Mandibular series – encases the Meckel’s cartilage

24. Splanchnocranium
 An ancient chordate structure associated with the filter feeding surfaces
 Arises from the neural crest cells departed from the sides of the neural tube and
migrate into the walls of the pharynx between successive pharyngeal slits
1. Meckel's Cartilage
2. Palatoquadrate
3. Rostrum
4. Labial Cartilage
5. Basihyal Cartilage
6. Ceratohyal Cartilage
7. Hyomandibular Cartilage
8. Ceratobranchial Cartilage
9. Basibranchial Cartilage
10. Hypobranchial Cartilage
11. A. Mandibular Arch
12. B. Hyoid Arch
13. C. Branchial Arch
Figure 2. Articulated chondrocranium and
splanchnocranium

25. Types of Jaw Attachments
1. Paleostylic – characteristic of Agnathans
- None of the arches attach directly to the skull
2. Euautostylic – the earliest jawed condition
- Found in Placoderms and Acanthodians
- The mandibular arch is suspended from the skull by itself without aid from the hyoid arch
3. Amphistylic – found in early sharks, some osteichthyians and crossopterygians
- Attached to the braincase through two primary articulations
- Anteriorly by a ligament connecting the palatoquadrate to the skull
- Posteriorly by the hyomandubula

26. 4. Hyostylic – found in most modern bony fishes
- The mandibular arch is attached to the braincase primarily through the
hyomandibula with the aid of the sympletic bone
5. Metautostylic – found in most amphibians, reptiles and birds.
- Attached to the braincase directly through the quadrate bone
- Formed in the posterior part of the palatoquadrate

27. 6. Craniostylic – found in mammals
- The entire upper jaw is a part of the braincase but the lower jaw called
dentary bone is suspended from the dermal squamosal bone of the
braincase
- The palatoquadrate and Meckel’s cartilages remain cartilaginous exceot at
their posterior ends which becomes the incus and malleus of the middle
ear respectively

28. Postcranial Skeleton
Axial
Appendicular
Function of body skeleton includes
- Protects the viscera
- Contributes to ventilation of the lungs
- Store for various minerals
- Provides rigidity to the body
- Provides series of firm and hinged segments needed for
locomotion in conjunction with the muscles

29. Axial Skeleton
Forms the main axis of the body
Composed of the notochord, vertebral
column, ribs, sternum and skull

30. Notochord
 The primitive axial skeleton,
replaced by the vertebral
column
 Unsegmented and composed
of dense fibrous connective
tissue
 The first skeletal element to
appear in the embryo of
chordates

31. Structure and Development of Vertebral Column
 The vertebral column is the
main axial support of vertebrates
 A vertebra is composed of a
centrum, one or two arches, and
various processes
 It protects the spinal cord and
provides rigidity to the body

32. Types of Vertebra Based on Centra
1. Aspondyly – no centra
2. Monospondyly – with only one centrum per
segment
- Stereospondyly – a monospondylous vertebra
in which the single centrum (intercentrum) is
separate
3. Diplospondyly – with two centra per segment
- Embolomerous – a diplospondylous vertebra in
which the approximate equal-sized centra are
separate
No centra

33. 4. Polyspondyly – with five to six centra per segment
5. Aspidospondyly – the centra and spines are separate
- Rhachitomous – an aspidospondylous vertebra with
numerous separate parts that constitute each
vertebral segment
6. Holospondyly – the centra and spines are fused into
a single bone
-Lepospondyly - a holospondylous vertebra with a
husk-shaped centrum usually pierced by a
notochordal canal.

34. Figure 2.33. Comparison of vertebrae of primitive
tetrapods and modern amniotes. The rachitomous type
(shown also in cross section, X.S.) occurred in
crossopterygians and in the earliest amphibians. B is from
a labyrinthodont in the reptile line. B1 and B2 are from
other labyrinthodonts. Whether the modern amphibian
centrum represents a hypocentrum (diagonal lines) or a
pleurocentrum (stippled) is not certain. The unmarked part
of the vertebra is the neural arch. Adapted, with
permission, from Kent, G. C. 4th ed. Comparative
anatomy of the vertebrates. St. Louis: C. V. Mosby Co.;
1978. [134]

35. Types of Centra Based on Shapes
1. Amphicoelous
2. Procoelous
3. Opisthocoelous
4. Heterocoelous
5. Acoelous

36. Structure and Function of Ribs
 Series of cartilaginous or elongated bony
structures served as attachment for the
vertebrae extending into the body wall
- Provide sites for secure muscle
attachment and help suspend the body
- Form a protective case (rib cage) around
viscera
- In Amniotes, contributes to the breathing
mechanism

37. Types of Ribs
1. True ribs – meet ventrally with the
sternum, consist of two jointed segments
 Vertebral or costal rib (proximal segment)
 Sternal rib (distal segment)
 Joint between costal and sternal ribs allows
changes in chest shape during respiration
2. False ribs – articulate with each other but
not with the sternum
3. Floating ribs – do not articulate ventrally

38. Structure and Function of Sternum
 A midventral skeletal element that usually articulates with the more anterior
thoracic ribs and with the pectoral girdle
 Strictly a tetrapod structure and primarily, and amniote characteristic
- Strengthen the anterior part of the trunk and body wall
- Helps protect the thoracic viscera
- Accommodates muscles of the pectoral limbs
- In amniotes, helps in ventilating the lungs
 The sternum forms either paired or midventral primodia that are regarded as
new structures not derived from the pectoral girdle or ribs

39. Appendicular Skeleton

40. Structure and Evolution of Median Fins
Occur in all jawless vertebrates and
fishes:
 Dorsal fins - located along the
middorsal line.
Anal fins - located between anus and
tail
Caudal Fin

41. DORSAL and ANAL FINS
o Prevent the body from turning around the
vertical axis (yawing) and around the longitudinal
axis (rolling).
o In primitive vertebrates, each fin is supported
within the contour of the body by a series of rod-
like radials or pterygiophores.
o The exposed membrane of fins of CEPHALASPIDS
and some PLACODERMS are supported only by
dorsal scales.

42. CAUDAL FIN
Classified into four types depending on size and shape of the spine.
1. Diphycercal – if the spine is straight to the tip of the tail
with equal dorsal and ventral lobe of the tail. (ex.
Cyclostomes, pleuracanths, and some sarcopterygians)
2. Hypocercal – if the spine tilts downward with longer
ventral lobe than dorsal lobe.(ex.anaspids)
3. Heterocercal – if the spine tilts upward with longer dorsal
lobe than ventral lobe.(ex.cephalaspids, placoderms, most
chondrichthyes, and primitive osteichthyes)
4. Homocercal - if all the fin membrane is posterior to the
spine with equal dorsal and ventral lobe.(ex.all teleosts)

43. Structures and Evolution of Girdles
Girdles of fishes
o the pectoral girdle is older, larger and more complicated
than pelvic girdle.
-It includes one or more cartilage or replacement
bones and several dermal bones derived from ancestral
scales and armour plates.
o Placoderms cartilaginous fins was related to overlying
plates of dermal skeleton.
o Cartiliginous fishes has no dermal elements
Scapulocoracoid – the right and left halves fused in
the midline forming a U-shaped girdle
1.Ceratotrichia
2. Scapulocoracoid Bar
3. Propterygium
4. Mesopterygium
5. Metapterygium
A. Basal Pterygiophores

44. Girdle and Tetrapod
o BIRDS have a bladelike scapula that
is oriented parallel to the spine.
- with large anterior coracoid
that is articulated with the sternum
- the posterior coracoid has
been lost
- two clavicles fuse ventrally
forming the furcula or absent in
some birds.

45. Girdle and Tetrapod
o the only membrane bone retained Therian
Mammals is the clavicle
- The anterior coracoid is completely lost.
- the posterior coracoid fuses to the scapula
forming the coracoid process of the scapula
- the scapula is unique in having spine which
represents its anterior border
- the ventral end of the spine is continued as
the acromion process to articulate with the clavicle.

46. Girdle and Tetrapod
o the pelvic girdle of Tetrapods is much enlarged over that of fishes and
is relatively uniform in basic structure.
-each half of the pelvic girdle is a single cartilaginous unit in the embryo.
-three bones are constant in the adult:
 a dorsal ilium, which articulates with one or more sacral vertebrae
 an anterior pubis
A posterior ischium
-the bones of one side usually fuse in the adult forming the innominate
bone
-one or both of the ventral bones of the two sides usually articulates of
fuse across the midventral line, the contact is called pelvic symphysis

47. Girdle and tetrapod
 Primitive amphibians had a solid,
triangular shaped pelvic girdle with the
ilium forming the apex
- the pubis can be distinguished
from the ischium by having a obturator
foramen that accommodates a nerve.
 In FROG, the girdle has a long, anteriorly
inclined ilium and cartilaginous pubis.

48. Girdle and Tetrapod
 REPTILES has various shapes patterned after
the basic plan of LABYRINTHODONTS
-the contact with the spine is firmer
-the large pubo-ischiadic fenestrum is present
between the two ventral bones
 Birds have a large pelvic girdle that is firmly
attached to the synsacrum
-the long ilium extends both anterior and
posterior to the socket for the femur or
acetabulum: The pubis is turned backward below
the ischium and there is no symphysis

49. Girdle and Tetrapod
 Mammals have a long and expanded ilium
extending only forward from the
acetabulum
- the large obturator fenestrum
represents both the obturator foramen and
the pbo-isichiadic fenestrum of the ancestor.
- a symphysis is always present
- MONOTREMES and MARSUPIALS have
epipubic bones that articulate with the
pubic bones extending forward in the
ventral body wall.

50. MISCELLANEOUS BONES
 SESAMOID BONE – bones embedded in or interrupting
tendon
 the largest is patella or knee cap
 Baculum (os penis) – bone in the penis of carnivores,
bats, insectivores, rodents, and some primates
 Additional small bones are found in the different
structures among TETRAPODS:
 in the eyelids of CROCODILIANS
 in the crest of a BIRD
 in the snout of PIGS
 at the base of the external ear of some RODENTS Baculum of a dog’s penis

51. TYPES of LOCOMOTION IN MAMMALS
 posterior limbs provide rapid acceleration and often support the greater
part of the weight.
 Types of locomotion
used by Tetrapods:
- GRAVIPORTAL
- CURSORIAL
- VOLANT
- AERIAL
- SALTATORIAL

52. TYPES of LOCOMOTION in MAMMALS
- AQUATIC
- FOSSORIAL
- SCANSORIAL
- ARBOREAL

53. Comparison of Vertebrates
Vertebrates Type of Skull Type of Jaw Attachment
Fishes Euryapsid Paleostylic/Hyostylic/
Amphistylic
Amphibians Anapsid Metautostylic
Reptiles Anapsid Metautostylic
Birds Diapsid Metautostylic
Mammals Synapsid Craniostylic
Type of Skull and Jaw Attachment

54. Girdles and Fins/Limbs
Dorsal and Caudal
Short/long bones
Hindlimbs are larger than forelimbs
Slightly broader and segmented
Uniform and specialized limb structure

55. Centra and Vertebral Column
Vertebrates Types of Centra based on
shape
Regions of Vertebral Column
Fishes Amphicoelus Anterior and Posterior (2)
Amphibians Amphicoelus, Procoelus or
Opisthocoelous
there is little or no regional specialization
of the vertebral column
Reptiles Procoelus 4 or 5 distinct region
Birds Heterocoelus consists of vertebrae, and is divided into
three sections: cervical (11-25) (neck),
Synsacrum (fused vertebrae of the back,
also fused to the hips (pelvis)), and
pygostyle (tail).
Mammals Acocoelus 5 distinct regions: Cervical, Thoracic,
Lumbar, Sacral and Caudal
Trunk and tail

56. Ribs and Sternum
Vertebrates Ribs Sternum
Fishes Dorsal and ventral set Absent
Amphibians Dorsal andventral set Some
(In early amphibians it is absent
xiphisternum; Anurans
omosternum)
Reptiles Cervical ribs Some
Birds Uncinate processes (are
extensions of bone that project
caudally from the vertical
segment of each rib)
Present
(Large:Carina)
Mammals only have distinct ribs on the
thoracic vertebra, although
fixed cervical ribs are also
Present
(sternebrae: modified into
manubrium and xiphisternum)
Most do not have ribs
Flight muscle

57. Girdles and Fins/Limbs
Vertebrates Girdles Fins/Limbs
Cartilaginous Fishes Large pectoral girdle Fins
Bony Fishes Increased girdle Fins
Amphibians Long girdle Limbs
Reptiles Various shapes Limbs
Birds Large pelvic girdle Limbs
Mammals Long and expanded Limbs